Why does the optim function return me a completely different value than scipy.optimize?

[Carl_97]

Hello, I've just started learning r language and I am rewriting some Python programs in r. I'm having a problem where r returns me very strange values for the same function when I use r's optim function:

optim(c(10,0.2,0.05),inputs)

and r returns like this:

  Nelder-Mead direct search function minimizer
function value for initial parameters = 590.694928
  Scaled convergence tolerance is 8.80204e-06
Stepsize computed as 1.000000
BUILD              4 99999999999999996863366107917975552.000000 -951.452736
Error in optim(c(10, 0.2, 0.05), inputs, control = list(trace = 3, maxit = 20,  : 
  objective function in optim evaluates to length 0 not 1
In addition: There were 50 or more warnings (use warnings() to see the first 50)

but if I write same function and use scipy.optimize.minimize function in python, python will returns me :

 final_simplex: (array([[1.19418799e+02, 3.70856099e-01, 8.34769615e-03],
       [1.19418799e+02, 3.70856099e-01, 8.34769615e-03],
       [1.19418799e+02, 3.70856099e-01, 8.34769615e-03],
       [1.19418799e+02, 3.70856099e-01, 8.34769615e-03]]), array([-946.69021452, -946.69021452, -946.69021452, -946.69021452]))
           fun: -946.6902145168723
       message: 'Optimization terminated successfully.'
          nfev: 438
           nit: 208
        status: 0
       success: True
             x: array([1.19418799e+02, 3.70856099e-01, 8.34769615e-03])

I have tested that the function in r and python is exactly the same, but the same optimal method return totally different result, anyone know what this is all about?(btw, I also try Matlab, give me same result as python.)
I also try different function, like x^2-2x+1, this kind of function r works well. Actually, I am working with log-likelihood function, so there exists log function, this might be the cause of the error?

Here is my function:

tail_body_likelihood <- function(r,params,pen){
    l = params[1]
    alpha = params[2]
    xmin = params[3]
    C = 2 - exp(-l * xmin)
    L = 0
    r = sort(r)
    f = sum(r < xmin)
    for (i in 1:f) {
        L = L - log(C) + log(l) - l*r[i]
    }
    for (i in (f+1):length(r)){
        L = L - log(C) + log(alpha/xmin) - (alpha+1)*log(r[i]/xmin)
    }
    Fbody = l*exp(-l * xmin) / C
    Ftail = alpha / (C * xmin)
    L = L - pen*(Fbody-Ftail)^2
    return(-L)
}
inputs <- function(x){
    a = tail_body_likelihood(b,x,10)
    return (a)
}

and here is the data.

[nirgrahamuk]

@Carl_97

I also try different function, like x2−2x+1x^2-2x+1 , this kind of function r works well. Actually, I am working with log-likelihood function, so there exists log function, this might be the cause of the error?

It does rather suggest that the code you wrote to represent the function in R is different from what you did in Python.
You haven't told us the function.